Kumis is a dairy product similar to kefir, but is produced from a liquid starter culture, in contrast to the solid kefir "grains". Because mare's milk contains more sugars than cow's or goat's milk, when fermented, kumis has a higher, though still mild, alcohol content compared to kefir.

Even in the areas of the world where kumis is popular today, mare's milk remains a very limited commodity. Industrial-scale production, therefore, generally uses cow's milk, which is richer in fat and protein, but lower in lactose than the milk from a horse. Before fermentation, the cow's milk is fortified in one of several ways. Sucrose may be added to allow a comparable fermentation. Another technique adds modified whey to better approximate the composition of mare's milk.[2]

A 1982 source reported 230,000 horses were kept in the Soviet Union specifically for producing milk to make into kumis.[8]
Rinchingiin Indra, writing about Mongolian dairying, says "it takes considerable skill to milk a mare" and describes the technique: the milker kneels on one knee, with a pail propped on the other, steadied by a string tied to an arm. One arm is wrapped behind the mare's rear leg and the other in front. A foal starts the milk flow and is pulled away by another person, but left touching the mare's side during the entire process.[9]

In Mongolia, the milking season for horses traditionally runs between mid-June and early October. During one season, a mare produces approximately 1,000 to 1,200 litres of milk, of which about half is left to the foals.[10]

Before fermentation, mare's milk has almost 40% more lactose than cow's milk.[12] According to one modern source, "unfermented mare's milk is generally not drunk", because it is a strong laxative.[1]Varro's On Agriculture, from the 1st century BC, also mentions this: "as a laxative the best is mare's milk, then donkey's milk, cow's milk, and finally goat's milk...";[13] drinking six ounces (190 ml) a day would be enough to give a lactose-intolerant person severe intestinal symptoms.

Traditionally, this fermentation took place in horse-hide containers, which might be left on the top of a yurt and turned over on occasion, or strapped to a saddle and joggled around over the course of a day's riding. Today, a wooden vat or plastic barrel may be used in place of the leather container.[14]

In modern controlled production, the initial fermentation takes two to five hours at a temperature of around 27 °C (81 °F); this may be followed by a cooler aging period.[15] The finished product contains between 0.7 and 2.5% alcohol.[16]

Archaeological investigations of the Botai culture of ancient Kazakhstan have revealed traces of milk in bowls from the site of Botai, suggesting the domestication of the animal.[19] No specific evidence for its fermentation has yet been found, but considering the location of the Botai culture and the nutritional properties of mare's milk, the possibility is high.

Now the Scythians blind all their slaves, to use them in preparing their milk. The plan they follow is to thrust tubes made of bone, not unlike our musical pipes, up the vulva of the mare, and then to blow into the tubes with their mouths, some milking while the others blow. They say that they do this because when the veins of the animal are full of air, the udder is forced down. The milk thus obtained is poured into deep wooden casks, about which the blind slaves are placed, and then the milk is stirred round. That which rises to the top is drawn off, and considered the best part; the under portion is of less account.[20]

This is widely believed to be the first description of ancient kumis-making.[4] Apart from the idiosyncratic method of mare-milking,[21] it matches up well enough with later accounts, such as this one given by 13th-century traveller William of Rubruck:

This cosmos, which is mare's milk, is made in this wise. […] When they have got together a great quantity of milk, which is as sweet as cow's as long as it is fresh, they pour it into a big skin or bottle, and they set to churning it with a stick […] and when they have beaten it sharply it begins to boil up like new wine and to sour or ferment, and they continue to churn it until they have extracted the butter. Then they taste it, and when it is mildly pungent, they drink it. It is pungent on the tongue like rapé wine when drunk, and when a man has finished drinking, it leaves a taste of milk of almonds on the tongue, and it makes the inner man most joyful and also intoxicates weak heads, and greatly provokes urine.[22]

Rubruk also mentions that the Mongols prized a particular variety of black kumiss called caracosmos, which was made specifically from the milk of black mares.

In the West, kumis has been touted for its health benefits, as in this 1877 book also naming it "Milk Champagne".

Toward the end of the 19th century, kumis had a strong enough reputation as a cure-all to support a small industry of "kumis cure" resorts, mostly in south-eastern Russia, where patients were "furnished with suitable light and varied amusement" during their treatment, which consisted of drinking large quantities of kumis.[23] W. Gilman Thompson's 1906 Practical Diatetics reported kumis has been cited as beneficial for a range of chronic diseases, including tuberculosis, bronchitis, catarrh, and anemia. Gilman also said a large part of the credit for the successes of the "kumis cure" is due not to the beverage, but to favorable summer climates at the resorts.[24] Among notables to try the cure were writers Leo Tolstoy and Anton Chekhov. Chekhov, long-suffering from tuberculosis, checked into a "kumis cure" resort in 1901. Drinking four bottles a day for two weeks, he gained 12 pounds, but no cure.[25]

Strictly speaking, kumis is in its own category of alcoholic drinks because it is made neither from fruit nor from grain. Technically, it is closer to wine than to beer because the fermentation occurs directly from sugars, as in wine (usually from fruit), as opposed to from starches (usually from grain) converted to sugars by mashing, as in beer. But in terms of experience and traditional manner of consumption, it is much more comparable to beer. It is even milder in alcoholic content than beer and is usually consumed cold. It is arguably the region’s beer equivalent.

Kumis is very light in body compared to most dairy drinks. It has a unique, slightly sour flavor with a bite from the mild alcoholic content. The exact flavor is greatly variable between different producers.

As indicated above, kumis is usually served cold or chilled. Traditionally it is sipped out of small, handle-less, bowl-shaped cups or saucers, called piyala. The serving of it is an essential part of Kyrgyz hospitality on the jayloo or high pasture, where they keep their herds of animals (horse, cattle, and sheep) during the summer phase of transhumance.

The capital of Kyrgyzstan, Bishkek, is named after the paddle used to churn the fermenting milk, showing the importance of the drink in the national culture.

The famous Russian writer Leo Tolstoy in A Confession spoke of running away from his troubled life by drinking kumis.[26] The Russian composer Alexander Scriabin was recommended a kumis diet and "water cure" by his doctor in his twenties, for his nervous condition and right-hand injury.

The popular Japanese soft drink Calpis models its flavor after the taste of kumis.[27]

^See also Nutritional Adaptation by O'Neil, Dennis, Palomar College: "In the Indian subcontinent and much of Central and Western Asia, dairy products are consumed frequently, but usually only after bacteria (lactobacilli) have broken down the lactose. After this has occurred, milk becomes yoghurt or kumis', both of which are relatively easily digested even by people who produce little lactase."